The control valve system of my invention is adaptable for a transmission of the kind disclosed in U.S. Pat. No. 4,767,384 of Richard D. Moan, which is assigned to the assignee of my present invention.
A continuously variable transmission usually includes adjustable sheaves and a chain or belt arranged between the driving sheave assembly and the driven sheave assembly. The driving sheave assembly may be connected to an internal combustion engine for a vehicle in an automotive vehicle driveline, and the driven sheave assembly may be connected through gearing and through a driveshaft and axle assembly to the vehicle traction wheels. By controlling the effective pitch radius of the sheave assemblies, the torque ratio can be varied between underdrive and overdrive. By appropriately calibrating the ratio changing characteristic and matching that characteristic with the speed/torque characteristic of the internal combustion engine, the powertrain package may achieve a minimum brake specific fuel consumption condition for each engine throttle setting.
The primary sheave assembly in a continuously variable transmission of this kind normally is used as the ratio controller, and the secondary sheave assembly normally is used to control belt loading. Each sheave assembly has a pressure operated servo with an expandable working pressure chamber. The servo is adjusted hydraulically to effect a change in the pitch radius of the sheave assembly. By varying the effective pressure on the primary sheave assembly, the ratio of the drive can be changed. The clamping force is controlled by maintaining an effective working pressure in the secondary sheave assembly.
A fluid pressure pump driven by the engine may be used as a pressure source for a control system that controls the adjustment of the primary servo and the secondary servo. A regulator valve in the control system in a preferred embodiment of the invention achieves the desired working pressure in the sheave assembly so that slippage of the belt or chain will not occur. A ratio control valve in the control system controls pressure distribution to the primary sheave assembly during ratio changes.